1. Field of the Invention
This invention relates to certain adamantanes, to methods for their synthesis and to their use as fuels, especially in volume-limited applications.
2. Description of the Prior Art
For volume-limited applications such as in air-breathing long-range cruise missiles and as the fuel component of bipropellant engines in rockets and space vehicles, the ideal fuel would have high density in order to provide for maximum range for a given fuel volume. It would also have a high heat of combustion and a high specific impulse. The ideal fuel would still further be easily ignited and reignited and stable to combustion. In situations where a liquid fuel was desired, the ideal fuel would have low viscosity, be liquid in at least the range of from about -54.degree. to about 74.degree. and would have low vapor pressure. Still further, the ideal fuel, whether liquid or solid, would be stable during storage, corrosion resistant and of low toxicity. Finally, the ideal fuel would be low in cost. No one fuel, of course, has all of the above properties.
In the past, hydrocarbon fuels, because they have high heats of combustion, have found wide use. However, for volume-limited applications hydrocarbon fuels have certain drawbacks. High density hydrocarbons (about 1.1 g/cc or greater) are expensive. Furthermore, high density hydrocarbons generally have rather high melting points and high viscosities. Bipropellant systems utilizing hydrocarbons are usually not hypergolic (do not ignite spontaneously when the fuel and oxidizer are brought together). Hydrocarbons generally have rather low specific impulses. Since hydrocarbons represent a simple two-atom system (C, H) their potential for structural variety is limited. Last but not least, hydrocarbons are insoluble in water and, therefore, any residual water in a system which contains hydrocarbons will separate out causing fuel line freezing problems in cold weather and accelerated corrosion owing to concentration of impurities in the water.
Amine fuels, because of their great structural variety (they have a three-atom system -- C, H and N), present an attractive alternate to hydrocarbons. A portion of an amine can be constructed from inexpensive, non-petroleum reactants, whereas the entire hydrocarbon is derived from petroleum. (Petroleum products are coming into ever shorter supply and will continue to do so as the World's petroleum reserves dwindle.) Most amines, and in particular, hydrazine and its derivatives, have higher specific impulses than hydrocarbons. Most bipropellant systems utilizing amines as the fuel component are hypergolic. Amine fuels, in some applications, have safety advantages over hydrocarbons. Those that are soluble in water and those that have densities greater than 1.0 g/cc may easily be extinguished in case of fire. The soluble ones simply dissolve and a burning dense amine sinks, permitting the fire to be smothered. Amines, however, like hydrocarbons have drawbacks.
One drawback of amines is that those with high density, like hydrocarbons, generally have high melting points and high viscosities (or are solids). Another drawback is that amines generally have lower gravimetric heats of combustion than hydrocarbons. These and other drawbacks have provided cause for continued experimentation in efforts to find materials with more good and less bad properties. Stated another way, the search goes on in efforts to find amines (or hydrocarbons or other materials) which are more suitable for use as fuels than those presently in use.